Depends if you want something lab based. For pharmacology you can go on to have a career in a lab as a research technician, but if you want a career where you run your own research programme in an academic, research or industrial setting its PhD time....
A pharmacology degree will still give you the option of non research jobs though such as finance, management, recruitment etc.
Pharmacy, of course you get the job guarantees and the immediate repectable salary, as well as indistrial jobs such as regulatory affairs (the paperwork for new drugs), clinical trials manufacturing etc, but if you want to do research its as above, and you do a PhD. However, if you do a PhD afterwards and you are a pharmacist, you can make extra money locuming, which is what I did before I got pissed off with the lot and decided to become a vet.
So I suppose its all down to whether or not you want a career running your own research unit...
For understanding, pharmacology iteself is quite biochemical, you need to be able to grasp receptors and enzymes as drug targets, and how their shape influences this. Depending on the course and the uni, you might be expected to do modules such as physiology, medicinal chemistry and drug design. biochemistry and other life sciences that complement the pharmacology bit.