Twenty-eight male volunteers were given either 1% delta 9-tetrahydrocannabinol (delta 9-THC) or vehicle alone (light mineral oil). They used the medication four times per day for one week. Five volunteers, four of which used vehicle alone, discontinued the study because of burning sensation and lid swelling. In the 23 volunteers who completed the study, there was no difference in intraocular pressure between eyes treated with 1% delta 9-THC and controls.