I think its important to note that the literature is very mixed regarding the relationship of self-reported cognitive complaints and actual neuropsychological (NP) performance. Complaints are often more related to depressive symptoms than to actual cognitive test performance, although some have found complaints to be associated with NP scores.
For example, see the following references:
Moore, D., Gonzalez, R., Heaton, R., Rippeth, J., Cherner, M., Grant, I., and the HNRC Group. (2001). Cognitive Complaints Neuropsychological Ability, and Depressive Symptoms in HIV. Journal of the International Neuropsychological Society, 7, 149.
Rohling ML, Green P, Allen LM, Iverson GL. Depressive symptoms and neurocognitive test scores in patients passing symptom validity tests. Arch Clin Neuropsychol. 2002 Apr; 17(3): 205-22.
Millikin CP, Rourke SB, Halman MH, Power C. Fatigue in HIV/AIDS is associated with depression and subjective neurocognitive complaints but not neuropsychological functioning. J Clin Exp Neuropsychol. 2003 Apr; 25(2): 201-15.
Kremer B, den Hartog HM, Jolles J. Relationship between allergic rhinitis, disturbed cognitive functions and psychological well-being. Clin Exp Allergy. 2002 Sep; 32(9): 1310-5.
Piazzini A, Canevini MP, Maggiori G, Canger R.. The perception of memory failures in patients with epilepsy. Eur J Neurol. 2001 Nov; 8(6): 613-20.
Antikainen R, Hanninen T, Honkalampi K, Hintikka J, Koivumaa-Honkanen H, Tanskanen A, Viinamaki H. Mood improvement reduces memory complaints in depressed patients. Eur Arch Psychiatry Clin Neurosci. 2001; 251(1): 6-11
Jorm AF, Christensen H, Korten AE, Jacomb PA, Henderson AS.. Memory complaints as a precursor of memory impairment in older people: a longitudinal analysis over 7-8 years .Psychol Med. 2001 Apr; 31(3):
Carter SL, Rourke SB, Murji S, Shore D, Rourke BP. Cognitive complaints, depression, medical symptoms, and their association with neuropsychological functioning in HIV infection: a structural equation model analysis. Neuropsychology. 2003 Jul; 17(3): 410-9. 441-9.
Higher depressive symptoms have been reported among MDMA users (which might be preexisting and/or related to use), and this could be associated with perception of cognitive (and other psychosocial) problems. It is also possible that substance users are generally more vigilant about their cognitive functioning and thus report more problems. In either case, self-selection bias among those who answer surveys or participate in such research continues to be a big problem for interpretation of findings.
That they did find decent correlations between reported level of MDMA and cannabis use and these memory complaints (after removing 84 respondents, of course) is more interesting but possibly still vulnerable to the issues above. For cannabis at least, meta-analyses of the literature suggest trivial long-term effects.
Papers showing cannabis causes minimal long-term effects:
Grant I, Gonzalez R, Carey CL, Natarajan L, Wolfson T. Non-acute (residual) neurocognitive effects of cannabis use: a meta-analytic study.J Int Neuropsychol Soc. 2003 Jul; 9(5): 679-89.
Gonzalez R, Carey C, Grant I. Nonacute (residual) neuropsychological effects of cannabis use: a qualitative analysis and systematic review. J Clin Pharmacol. 2002 Nov; 42(11 Suppl): 48S-57S.
In our research group, we found better NP performance among methamphetamine dependent study participants who also smoked pot.
Gonzalez R, Carey C, Moore DJ, Schweinsburg BC, Rippeth J, Heaton RK, Cherner M, Grant I, and the HNRC Group. (2002). Effects of cannabis use on the cognitive performance of methamphetamine dependent individuals. Journal of the International Neuropsychological Society, 8 (2), 287-288.
That's my 2 cents. Stay alert.
PhD Assistant Adjunct Professor
Department of Psychiatry
HIV Neurobehavioral Research Center
University of California San Diego