The risk of DVT is raised
slightly by smoking (That's smoking anything, not just tobacco), about the same amount as a FAAB person has on the pill, so it's worth keeping an eye on, but not actually as terrifyingly common as we're led to believe.
You're at higher risk if you smoke habitually/regularly, especially if you don't do any cardio style exercise. The occasional blaze wouldn't be the worst thing, but you may want to have a look around at other options that don't involve combustion, like vaporising.
Depends what you want out of it, really. I smoke a small amount, but then I run, walk a lot, have a decent diet etc. I've not had any problems so far, long may that continue! Life is, in general, about taking measured risks and deciding for yourself what you think is acceptable.
In my opinion, the occasional blunt would be fine, but you're the one who knows your medical situation and how healthy your lifestyle is, so definitely don't take my word for it....I am NOT a doctor!