Reinforcing, subjective, and performance effects of lorazepam and diphenhydramine in humans

The reinforcing, subjective, and performance effects of 400 mg diphenhydramine (D), 4 mg lorazepam (L), and placebo (P) were compared across repeated administrations in 12 healthy, adult male participants with histories of recreational sedative abuse. P, L, and D were administered orally in a block, random sequence 4 times each. L and D increased scores on participants' liking of the drug, desire to take the drug again, and monetary value of the drug relative to placebo. D increased ratings on scales of unpleasant somatic side effects. When the choice was between D and P or between L and P, choice between D and L was greater than chance, and choice of P was less than chance. When the choice was between D and L, both drugs were chosen an equal number of times. L and D effects were consistent across repeated administrations. Correlational analysis showed that some subjective measures were positively correlated, whereas other measures were negatively correlated with measures of drug reinforcement.