Afaik, it depends on where the medicine came from, if it's from a eukaryote (compounds from plants, fungi, animals) then it may be glycosylated, and you'd therefore have to produce it in a host that supports glycosylation (another eukaryote). I think prokaryotes also have some features of transcription and translation that make them different to eukaryotes, but I can't remember off the top of my head.

But to be honest, I think the point of this may be that growing stuff in a plant is easier than using a bioreactor or flask.

For a plant, you need:

• Soil
• Water
• Light
• A bag of seeds

For a bioreactor you need:

• A bioreactor (not cheap)
• Sterilisation equipment
• Closed processing equipment (tubes, filters, tube welders)
• Bioreactor control device
• Biological safety cabinet to work in
• Sterile media, probably with specific additives depending on your cell line
• All of the numerous plastic consumables used in modern labs
• Liquid nitrogen storage of cells
• Probably some more stuff

Dunno about you, but the former sounds easier to do in a space station to me.