First, it's important to note that in antiquity fibrous cannabis and drug oriented cannabis are hard to separate. Hemp was a huge part of life, being used to make clothes, oil, and even paper. Hemp stalks contain fibers, whereas the flowers are heavier in active compounds that can cause drug-like effects. Since it has a high genetic variability, local strains can differ a good bit, however most ancient cannabis bred for fiber use was probably relatively low in THC and other psychoactive compounds (but higher than modern hemp plants which have been specifically bred for lack of THC). It was used for medicinal and recreational purposes in places like China, India, and Scythia. European records generally lack the awareness of hemp's possible use as a drug (Herodotus mentioned it, but only as something other people not in Greece were doing), whereas ancient Arabic texts record use of hashish and other strong cannabis-based drugs. This suggests that the strains common to Europe and the western Mediterranean may have had lower concentrations of cannabinoids. Since hemp originated in China, it makes sense that Asian and Middle Eastern cultures would have had more time to selectively breed more interesting hemp varietals, whereas European cultures that got on the hemp train later had to catch up. At the very least, ancient Italians did put hemp in their mouths- we have dental records of people with distinctive grooves in their front teeth and micro-fragments of hemp material. This was probably in order to make thread, rather than get high, however the taste must not have been too bad.

The most relevant source I found was probably this one, Cannabis in the Ancient Greek and Roman World. It states that Pliny the Elder's writings on hemp say that stalks are used for fiber while flowers are dried and used for other things- a process that could easily have cannabis results. Dioscorides, a doctor, mentions hemp as a medicine (a lot of stuff got used as medicine in Ancient Rome, regardless of efficacy, so the fact that it was being used as medicine doesn't mean it was being used correctly). In general there seems to be a solid awareness of cannabis as a remedy, and a more abstract sense that it could be used socially (Galen commented on this use). Some researchers, like Patrick McGovern suggest that it may have been regularly mixed into wine, while others point to cannabis use in Egypt and other earlier civilizations as evidence that the Romans probably had a good idea of the effects of the plant. I personally take a more hesitant approach and assume that it's use was moderate to minimal. Since wild cannabis plants were not native to the area, the chances of people stumbling on higher THC variants rather than cannabis grown for fiber were lower, and the use of hemp in clothing, rope making, and oil probably overshadowed other uses. Plus, people were way more into opium. Nevertheless, you can't underestimate the willingness of our ancestors to try to use things to get high, so it definitely got experimented with. You can't have all those flowers around and not try to smoke them.

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