As everyone said, try to go here on a weekday morning. The aisles are small and I think if I had…read moregone a bit later in the day, I would have been incredibly overwhelmed as even with few people, there wasn't much space.
People recommend CityPharma as the cheapest pharmacy all over Tiktok and Reddit. From going into multiple smaller pharmacies (probably 10+) and also comparing prices with Pharmacie du Forum Des Halles (much larger store with larger selection) and comparing with Pharmacie Monge Notre Dame, the prices were more or less the same between these 3 larger pharmacies (some products would be a few cents or a euro cheaper at one or the other for each pharmacy listed). The prices are definitely more expensive at the smaller pharmacies unless you find a special deal on a specific product. CityPharma sometimes has special deals for buying multiple products of a certain brand, but there were none when I went.
If you want a more leisurely, spacious, and calm shopping experience, I would recommend going to Pharmacie du Forum Des Halles since there is way more space and employees to help you and prices are similar.