The two main ways I have found that I can guarantee vivid dreams are -
1: If I am travelling and sleeping in a strange bed
2: If I am sick with a bad cold or flu my dreams will be especially vivid and memorable
Short of being sick or hitting the road are there any ways to force vivid dreams?
Eat a large amount of cheese an hour or so before bed. It’s a cliche but true.
Drink lots of booze or smoke lots of weed every day over the course of a week or two, then stop. That works too.
Taking Prozac (Fluoxetine) typically causes extremely vivid dreams as a side effect for the first few weeks.
Similarly, ingestion of MDMA can cause vivid dreams for a few days afterwards. This is because both flood the brain with serotonin, albeit in different ways.
Snorting nutmeg (I strongly do not recommend this, by the way, and not only because it is toxic in high doses) caused little effect on me while awake but I did have very realistic, very weird dreams that night.
So in my experience, various drugs that increase serotonin levels will make your dreams more interesting. YMMV.
Chocolate causes me to have vivid dreams very consistently.
When I was on nicotine patches, leaving them on while I slept gave me weird dreams.
There’s also a workout recovery supplement called ZMA (it’s essentially zinc, magnesium and b6) that is supposed to help you sleep deeper and thus recover better, and I had wacky dreams because of the vitamin b6, but you’ve got to take it at the right time before going to bed.
Ny-quil gets me every time.
I get them more in winter when it is still dark at waking up time.
I had vivid dreams as a side effect of Aleve (naproxen sodium). I used to take Aleve at night for carpal tunnel pain, and the dreams were a pleasant side effect. I had to stop after I had an ulcer my doctor attributed to NSAIDs like Aleve.
I have more vivid dreams when I’m either in the middle of learning something difficult, or when I’m getting more sleep than normal (particularly by sleeping in in the mornings). Those are non-pharmacological options that work for me, but I tend to remember having vivid dreams pretty often anyway, so they might not work for everyone.
Oh, and pregnancy has worked for me so far. I’ve had even more crazy-ass dreams than normal since I got pregnant. Obviously this is not generally an option. 
It is an incredibly dramatic effect that lasts a few nights following total cessation of use. I’ve been told.
Me too.
Vicodin. Extremely vivid dreams and the worst constipation ever.
Me too, the dreams were amazing but they were so vivid and seemed so real that I’d wake up feeling like I hadn’t even really slept. After a few days of feeling tired as hell I started taking them off at night.
My mom had the same problem with nicotine patches, except hers were mostly nightmares. She’d wake up sweating and shaking and crying - it was terrible. She gave up on that after a week.
I’ve found drinking sleepy time type teas do this to me. Anything that I get at the tea shops that is meant to help you sleep better (sweet dreams, sleepy time etc) if I drink before bed I am guaranteed vivid dreams.
Synthroid does the trick - they’re not only vivid, they’re seriously fucked up.
However, I probably wouldn’t suggest this unless you actually have a thyroid issue.
Personal experience - Lexapro.
Scientific study (difficult to reproduce at home) - systematically deprive yourself of REM sleep for few days time (of JUST REM sleep, not total sleep time) and then let yourself sleep normally again. You’ll get a “hit” of a few days to a week of really vivid dreams as you catch back up on your REM.
Our brains crave REM desperately, and when deprived, will skip other phases of sleep to get to REM faster, hit REM deeper, and stay longer, therefore producing much more memorable and intense dreaming sessions.
It does work quite well - I was able to learn to lucid dream over about a week’s work through this method, but it’s hell on your waking life, and I doubt that I would be able to do it again now and keep up with my schedule.
Studies are mixed, but there are a few indications that systematic long-term REM deprivation is really not so good for people. However, some anti-depressants suppress REM nearly entirely, and seem to not cause too much damage.
http://www.psychlotron.org.uk/resources/sleep/AQA_A2_sleep_deprivationstudies.pdf
Check out the second section there (pg 2) on selective deprivation of REM on animals (the cat died) and humans (they basically front-loaded REM until they caught back up).
Melatonin helps. Sometimes I get them, sometimes I don’t.
Ugh. That stuff makes me hyper and jumpy, but if I do manage to get to sleep after taking it, I generally dream vividly. Unfortunately, they are invariably vivid nightmares.
Another one for melatonin. I already have vivid dreams as it is but when I take some of those, whoo! Crazy.