I'm very familiar with what it's like to have scenes that your players don't experience in a game, as I've worked as a dev before and am currently a writer for an adult game. The one I'm currently working on is intended as a broad appeal game, so we actually don't intend for any given player to experience more than half of the scenes in the game due to it being content they just aren't into. Less actually, due to branching paths. Every sex scene is optional, even if that might be somewhat detrimental to the story as it's a sacrifice we have to make for this to be a game people can fap to. The upside is that there's more players and each scene usually has some people who say it's their favorite. The romantics are in love with a, the gay fans lust over b, the folks into extreme kink x are into c. Completionists are our bane, when they insist that they need to see the pairings they don't like (say m/m) or the more extreme kinks they're not into. Then they complain about it.
I've seen two main ways to build an adult game. Broad appeal and niche appeal. In a broad appeal game, you usually make everything optional and clearly signposted (or have content toggles), have a wide variety of fetishes, and have a lot of vanilla or fairly universally appealing content to tide people over between the kinkier stuff they're really into. Niche appeal games generally pick one specific kink or group of kinks that they focus on. Nearly all of the content in the game has that particular kink and is free to make that content mandatory as the player gives the okay for that content when they started the game and the bulk of the content is about that one kink. Anything that isn't about that main kink should be optional and clearly signposted. These aren't hard rules; for example a broad appeal game can have optional sections of the game that focus on one kink that isn't optional, assuming it's signposted. They are useful guidelines.
An adult game that forces players to see content they don't like isn't useful as fapping material. It doesn't matter how well written it is if that kink is a turn off. Human sexuality is stupid complicated and players will be much better at understanding their sexuality than a developer can possibly be. That's why content lists are so important. They tell players, 'this is a game you can fap to' or, 'this is a game you can't fap to.' It's just as important that player can find what they like as it is for them to avoid what they don't like. Using the broad and niche appeal guidelines helps you maximize the number of players that enjoy your game.
Bringing this around to your game, you could do something like having big breasts, the drugs, and m/f be the focus of the game. You are up front about this in the advertising and main menu, so players give permission for that content when they click start. Then you can go nuts with that kind of content in the game itself and it's totally fine. Even have major plotlines of the game use that as critical parts of the storytelling, like the ship's crew getting addicted to the drugs and exploring how that affects their relationships with one another and character development as a result of it. Just don't blindside people with unexpected or unavoidable content unrelated to the central themes. Alternatively, you can pull back from this and instead give players choices over who they get involved with and who's kinks they want to see. The game explains to them in some way that the doctor's content focuses on the drugs and it's up to the player whether or not they want to pursue that relationship path and engage with the drugs. If they choose not to, then they don't get the drug content.
