delivered the opinion of the court:
On August 23, 1979, the petitioner, Andre Jones, pleaded guilty to three counts of first degree murder. On April 15, 1980, petitioner was sentenced to death. Petitioner currently appeals from a St. Clair County circuit court order dismissing his third post-conviction petition without an evidentiary hearing. Because petitioner was sentenced to death, this court has jurisdiction over the instant appeal pursuant to Supreme Court Rule 651(a) (134 Ill. 2d R. 651(a)). We affirm.
BACKGROUND
Petitioner pleaded guilty in the circuit court of St. Clair County to three counts of first degree murder. A jury sentenced petitioner to death for each of the murder convictions. On direct appeal, this court affirmed petitioner’s convictions and two of his death sentences. We vacated petitioner’s third death sentence, however, and *357remanded for imposition of a sentence other than death on that conviction. People v. Jones, 94 Ill. 2d 275 (1982). The United States Supreme Court denied petitioner’s petition for writ of certiorari. Jones v. Illinois, 464 U.S. 920, 78 L. Ed. 2d 264, 104 S. Ct. 287 (1983).
Petitioner subsequently filed a petition for post-conviction relief in which he alleged that he received ineffective assistance of counsel at both the guilty plea stage and at sentencing. The circuit court dismissed the post-conviction petition without an evidentiary hearing, and we affirmed, holding petitioner’s claims were barred by res judicata because they could have been raised on direct appeal but were not. People v. Jones, 109 Ill. 2d 19 (1985). Petitioner filed a second post-conviction petition alleging his attorney on direct appeal and in the first post-conviction proceedings was ineffective for failing to challenge the competency of his trial attorney. After conducting an evidentiary hearing, the circuit court denied petitioner’s second post-conviction petition. Once again, we affirmed. People v. Jones, 144 Ill. 2d 242 (1991).
Petitioner then filed a petition for a writ of habeas corpus in federal court. The district court dismissed the petition (Jones v. Welborn, 877 F. Supp. 1214 (S.D. Ill. 1994)), and the Seventh Circuit Court of Appeals affirmed (Jones v. Page, 76 F.3d 831 (7th Cir. 1996)).
Petitioner subsequently filed a third post-conviction petition, which is the subject of this appeal. In this petition, petitioner alleges that his due process rights under the United States and Illinois Constitutions were violated when the trial judge failed to conduct a fitness hearing based on petitioner’s ingestion of psychotropic drugs at the time of his plea and sentencing. Petitioner also alleges that his trial counsel was ineffective for failing to request such a fitness hearing. The circuit court dismissed the post-conviction petition without an evidentiary hearing.
*358ANALYSIS
The Post-Conviction Hearing Act contemplates the filing of only one post-conviction petition. People v. Flores, 153 Ill. 2d 264, 273 (1992); People v. Free, 122 32044078683695. 2d 367, 375 (1988). Moreover, section 122 — 3 of the Act provides that “[a]ny claim of substantial denial of constitutional rights not raised in the original or an amended petition is waived.” 725 ILCS 5/122 — 3 (West 1998); Flores, 153 Ill. 2d at 274; Free, 122 Ill. 2d at 375-76. A ruling on an initial post-conviction petition has res judicata effect with respect to all claims that were raised or could have been raised in the initial petition. Flores, 153 Ill. 2d at 274; Free, 122 Ill. 2d at 376. Consequently, defendant faces a daunting procedural hurdle when bringing a successive post-conviction petition. People v. Jones, 191 Ill. 2d 194, 198 (2000).
In Flores, this court held that the procedural bars of waiver and res judicata may be relaxed with respect to successive post-conviction petitions only under certain circumstances. Under the “cause and prejudice” test announced in Flores, claims in a successive post-conviction petition are barred unless the petitioner can establish good cause for failing to raise his claims in prior proceedings and actual prejudice resulting from the claimed errors. Flores, 153 Ill. 2d at 279. For purposes of this test, “cause” is defined as “ ‘ “some objective factor external to the defense [that] impeded counsel’s efforts” to raise the claim’ in an earlier proceeding” (Flores, 153 Ill. 2d at 279, quoting McClesky v. Zant, 499 U.S. 467, 493, 113 L. Ed. 2d 517, 544, Ill S. Ct. 1454, 1470 (1991), quoting Murray v. Carrier, 477 U.S. 478, 488, 91 L. Ed. 2d 397, 408, 106 S. Ct. 2639, 2645 (1986)) and “prejudice” is defined as “an error which ‘ “so infected the entire trial that the resulting conviction violates due process” ’ ” (Flores, 153 Ill. 2d at 279, quoting United States v. Frady, 456 U.S. 152, 169, 71 L. Ed. 2d 816, 831, 102 S. Ct. 1584, *3591595 (1981), quoting Henderson v. Kibbe, 431 U.S. 145, 154, 52 L. Ed. 2d 203, 212, 97 S. Ct. 1730, 1737 (1977)).
We need not decide whether petitioner’s first claim, that the trial court violated petitioner’s due process rights when it failed to conduct a fitness hearing based on petitioner’s ingestion of psychotropic drugs, is procedurally barred because this claim is not a constitutional claim which is cognizable in post-conviction proceedings. People v. Mitchell, 189 Ill. 2d 312, 328-29 (2000) (holding a trial court’s failure to conduct a fitness hearing under section 104 — 21(a) of the Code of Criminal Procedure of 1963 when a defendant is taking psychotropic drugs at trial or sentencing does not constitute a violation of due process, and, therefore, is not a cognizable claim in post-conviction proceedings).
Petitioner’s ineffective assistance of counsel claim, unlike petitioner’s first claim, is cognizable in post-conviction proceedings. Therefore, we must determine whether petitioner’s claim is procedurally barred. Applying the cause and prejudice test to the instant case, it is clear that petitioner remains procedurally barred from bringing this ineffective assistance of counsel claim in his third post-conviction petition. Even if petitioner could establish cause for failing to raise his claims earlier, he cannot establish prejudice resulting from his trial counsel’s failure to request a fitness hearing.
The record in this case belies petitioner’s assertion that his trial counsel was ineffective for failing to request a fitness hearing in light of petitioner’s ingestion of psychotropic drugs and his history of mental illness. Cheryl Prost, a psychologist, evaluated petitioner before and after he entered his guilty plea and concluded that petitioner was sane at the time he committed the murders and that he was fit to stand trial. Jones, 144 Ill. 2d at 258. In a report filed with the trial court one week after petitioner pleaded guilty, Prost reached the following conclusion:
*360“No pathology was found concerning psychosis or mental retardation nor significant substance abuse. What has been found is a very pathological personality disorder which has been present since childhood and which has not changed through the efforts of numerous state penal institutions. Mr. Jones has had poor control over his anger and impulsiveness as well as had little respect for the rights and lives of others.”
Dr. Peter R Heinbecker, a psychiatrist, examined petitioner when he confessed to two additional murders prior to his sentencing hearing. Dr. Heinbecker also concluded that petitioner was sane at the time of the murders for which he pleaded guilty and that petitioner was fit for trial. Jones v. Page, 76 F.3d at 843-44, 846.
The primary support for petitioner’s claim that his trial counsel was ineffective for failing to request a fitness hearing is an affidavit from Dr. Michael M. Gelbort. Dr. Gelbort determined that petitioner’s verbal and performance IQ’s are at the “lowest end of the low average range” and that petitioner suffers from a number of cognitive impairments, including attention deficit disorder. None of this evidence, however, establishes that there was a bona fide doubt of his fitness or a reasonable probability that petitioner would have been found unfit if a fitness hearing had been conducted. See Mitchell, 189 Ill. 2d at 333-34. Thus, we conclude that petitioner has failed to establish that his trial counsel’s failure to request a fitness hearing infected petitioner’s trial to such a degree that his resulting conviction violated due process. Since petitioner is unable to satisfy the prejudice prong of the cause and prejudice test, he is procedurally barred from bringing this claim in a successive post-conviction petition.
Finally, petitioner argues that it would be fundamentally unfair and unconstitutional to execute him without conducting an evidentiary hearing on his post-conviction petition. Petitioner asserts that his 30-year history of *361mental illness necessitates an evidentiary hearing on his claims. We disagree. A post-conviction petitioner is not entitled to an evidentiary hearing as a matter of right; the Act requires an evidentiary hearing only when the petitioner makes a substantial showing of a violation of his constitutional rights. People v. Hobley, 182 Ill. 2d 404, 427-28 (1998). Petitioner has failed to make such a showing.
CONCLUSION
For the reasons stated, the judgment of the circuit court of St. Clair County dismissing petitioner’s third post-conviction petition without an evidentiary hearing is affirmed. The clerk of this court is directed to enter án order setting Tuesday, November 21, 2000, as the date on which the sentence of death entered in the circuit court of St. Clair County is to be carried out. The petitioner shall be executed in the manner provided by law (725 ILCS 5/119 — 5 (West 1996)). The clerk of this court shall send a certified copy of the mandate in this case to the Director of Corrections, to the warden of Tamms Correctional Center, and to the warden of the institution where defendant is now confined.