Eich et al. (1975) gave research participants a learning task while the participants were under the influence of nicotine or marijuana and tested memory later, under the same drug or the other drug. he found that

He found that when if participants were sober while studying words and when they were tested on them they achieved best results. 
Worts results where achieved when participants were under the influence of the drug when studying but sober when at the test.
When people were drugged at both study and the test they recalled more words than when they were drugged during the study and sober at the test.
And finally, when people were tested while under influence of marijuana but studied sober they actually performed worse than when tested sober.

So you know what happened and so it doesn’t repeat it’s self