How to normalize these 3 tables?

Hi, I was given 3 tables and am wondering how to normalize or restructure them:

table PROJECT:

project_id	integer primary key
project_name	varchar2(20)

table DRUG:
drug_id		integer primary key
drug_project_id	integer foreign key drug_project(drug_project_id)

table DRUG_PROJECT:
drug_project_id	integer primary key
project_id	integer	foreign key project(project_id)
drug_id		integer foreign key drug(drug_id)

The reason I have drug_project is because the same drug can associate with different projects and I would like to have an unique id for each. But it looks like it won't work since I have to foreign keys pointing each other on 2nd and 3rd tables.

I appreciate your help. Thanks!

Susana

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