Hmm this one's hard to answer. First, what is pharmaceutical science? It's a very broad field encompassing many disciplines... basically anything to do with drugs. Pharmaceutical scientists are people who are experts in the sciences necessary for drug discovery/development.

There are people finding new ways to synthesise drugs/enhance drug potency/reduce drug side effects via chemistry - these are your medicinal chemists.

There are people finding new ways to deliver drugs to site of interests (like cancer cells but not normal cells), new ways to improve absorption, increase brain penetration, reduce drug elimination from the kidneys - these guys are involved in formulation science, biopharmaceutics, nanotechnology, powder technology etc.

Then we have people who investigate cell signalling that may be involved in disease that can be targeted by drugs, study effects of drugs in animals/isolated organs/tissues/cells, study differential gene/protein expression before/during disease and after drug treatment, study how receptors interact with drugs - these people are involved in pharmacology, molecular biology, genetics, cell biology etc. There are people who classify themselves according to the medical field they're in eg. neuropharmacologist, neuroscientist, cardiovascular pharmacologist, immunologist and they can be involved at every level of science - from molecular biology to animal pharmacology.

In truth, scientists in academia are flexible to some extent - they use whatever techniques necessary (from mutating proteins to cannulating rat carotid arteries) to answer the questions in their research.

Biochemistry, like the name suggests, studies chemistry in the biological setting. It's somewhat related to molecular biology. Biochemistry deals with the finer details as opposed to say tissue/animal/behavioural pharmacology which studies (for example) physiological/behavioural changes after drug administration. Biochemists work with proteins, peptides, genes, metabolic substrates etc. If biochemists work in the context of drug discovery, then I don't see why they can't be called pharmaceutical scientists as well. E.g. if they are studying receptor (protein) structure-function (amino acids) relationships in the context of drug binding or maybe studying how a certain enzyme interacts with a certain substrate in a certain pathway and how to get a drug to interfere.