Timothy Leary, Flashbacks, 1990, p251-253:

• The lunch with Marshall McLuhan at the Plaza [Hotel in New York, apparently in the summer of 1966]¹ was informative. “Dreary Senate hearings and courtrooms are not the platforms for your message, Tim. You call yourself a philosopher, a reformer. Fine. But the key to your work is advertising. You’re promoting a product. The new and improved accelerated brain. You must use the most current tactics for arousing consumer interest. Associate LSD with all the good things that the brain can produce — beauty, fun, philosophic wonder, religious revelation, increased intelligence, mystical romance. Word of mouth from satisfied consumers will help, but get your rock and roll friends to write jingles about the brain.” He sang: “Lysergic acid hits the spot / Forty billion neurons, that’s a lot.”
• “Your advertising must stress the religious. Find the god within. This is all frightfully interesting. Your competitors are naturally denouncing the brain as an instrument of the devil. Priceless!”
• “To dispel fear you must use your public image. You are the basic product endorser. Whenever you are photographed, smile. Wave reassuringly. Radiate courage. Never complain or appear angry. It’s okay if you come off as flamboyant and eccentric. You’re a professor, after all. But a confident attitude is the best advertisement. You must be known for your smile.”²
• “You’re going to win the war, Timothy. Eventually. But you’re going to lose some major battles on the way. You’re not going to overthrow the Protestant Ethic in a couple of years. This culture knows how to sell fear and pain. Drugs that accelerate the brain won’t be accepted until the population is geared to computers. You’re ahead of your time. They’ll attempt to destroy your credibility.”
• The conversation with Marshall McLuhan got me thinking further along these lines: the successful philosophers were also advertisers who could sell their new models of the universe to large numbers of others, thus converting thought to action, mind to matter. I devoted several days and one acid trip to analysis of the packaging of previous American revolutions: “Give Me Liberty Or Give Me Death,” “A Nation Cannot Exist Half Slave and Half Free,” “We Have Nothing to Fear But Fear Itself.” “Lucky Strike Means Fine Tobacco.” One morning, while I was ruminating in the shower about what kind of slogan would succinctly summarize the tactics for increasing intelligence, six words came to mind. Dripping wet, with a towel around my waist, I walked to the study and wrote down this phrase: “Turn On, Tune In, Drop Out.” Later it became very useful in my function as cheerleader for change.
• Turn On meant go within to activate your neural and genetic equipment. Become sensitive to the many and various levels of consciousness and the specific triggers that engage them. Drugs were one way to accomplish this end. Tune In meant interact harmoniously with the world around you — externalize, materialize, express your new internal perspectives. Drop Out suggested an active, selective, graceful process of detachment from involuntary or unconscious commitments. Drop Out meant self-reliance, a discovery of one’s singularity, a commitment to mobility, choice, and change.

A report in the Santa Cruz Sentinel, ‘Liddy vs Leary‘, from Aril 9, 1982, has this:

Leary, invoking the ideas of Marshall McLuhan, expressed the view that “education, entertainment and advertising must go together.” “Entertainment means holding someone’s attention,” he said. “It means making my position more attractive.”