Pleasure and happiness aren't the same thing, but most people chase pleasure while calling it happiness. Pleasure is the quick hit—good food, sex, scrolling your phone—it feels great but fades fast. Happiness is something else entirely, and what it means changes drastically depending on how smart you are. Less intelligent people tend to equate happiness with basic pleasures and getting their needs met. Average intelligence ties it to status, money, keeping up with others. But higher intelligence complicates everything: some people find meaning in ideas, creativity, or purpose; others overthink themselves into misery, seeing through all the goals that used to motivate them. Intelligence gives you better tools to understand happiness but can also strip away the simple certainties that make it easier to actually feel happy. You gain clarity but lose the blissful ignorance that makes chasing straightforward goals satisfying.
Pleasure is happiness. If you could afford it you can have great food, unlimited sex, free time to pursue passions and interests and most importantly endless, unrestricted power over people all the time. The above, combined with no stressors will pretty much guarantee life long happiness.
The only caveats are drugs (generally destructive) and clinical depression caused by hormonal imbalances.
Pleasure is immediate, whereas happiness (or joy) reflects something more long-lasting and is often ineffable.
You can get used to pleasure because you can predict it and control it. Joy and wisdom are not gained so easily, and it's that challenge that creates meaning.
If you had a brain scan of pleasure and a brain scan of happiness, do you think they'd be identical?
I think you understand that unbridled pleasure eventually leads to jadedness, because you excluded drugs. The other forms of pure pleasure do the same thing but over a longer timescale. Yes, you'd have a truly amazing time at first. Why do a lot of rich people turn to drugs or gambling?