Inhibition of prostaglandin synthetase by limonoids ( and / or polysaccharides ) reduces perceived pain. Neem leaf and bark extracts have been shown to be a more potent inhibitor of prostaglandin syntetase than acetylsalicylic acid ( aspirin ) and pethidine hyidrocloride. In same cases neem was effective at reducing pain for a significantly longer period than standard agents. Neem also reduces the activity of the central nervous system, which also reduces perceived pain. According to a study led by N. Khanna, neem produces and analgesic effect upon the central and peripheral neural pathways. He also feels that both opioid and non-opioid receptors can be affected by neem.