The use of natural health products (NHPs) within the HIV community is high. Several NHPs have demonstrated interactions with HIV medications that could contribute to drug failure. We aimed to conduct a systematic review of clinical trials examining NHP–HIV drug interactions and their methodological characteristics. We searched electronic databases and unpublished resources independently, in duplicate. Nine studies were identified, eight clinical pharmacokinetics trials and one population-pharmacokinetics trial. Investigators studied four different herbal medicines (St John's wort, garlic, goldenseal and milk thistle) and one vitamin (vitamin C). Significant interactions were observed with St John's wort, garlic and vitamin C. However, methodological challenges exist to making the results directly generalizable to patients. This review finds that important drug level changes exist when NHPs are combined with HIV medications. Considering patient values and the implications of these studies, further research is urgently required to determine the extent of interactions with other commonly used NHPs.