Studies using a specific model such as IPRIA , MICIPR  and Akalephaan et al.  also suffer from the lack of control of good cofactors, as these models are macro-economic in nature. All of these models used simulations based on common assumptions, i.e. constant growth rates of macroeconomic variables and generic and innovative drugs, which are perfectly replaced. European Commission (2018). EU-Vietnam trade and investment agreement. Brussels, 38-39. Available at address: Some ex ante studies have assessed the impact of the well-being of a stronger IP system. Chaudhuri et al.
 estimated that annual welfare losses to the Indian economy would be in the order of US$450 million by the withdrawal of generic drugs from the Quintolon sub-segment market. Similarly, Dutta  estimated the total consumer loss to $378.5 million due to the application and deregulation of prices on the market of 43 drugs in India, and this decline in consumer well-being would be significantly mitigated by price regulation. This means that patent monopolies are less effective as a means of price increases if the government actually regulates prices. Stevens H, Huys I. Innovative approaches to improving access to medicines in developing countries. Before Med (Lausanne). doi.org/10.3389/fmed.2017.00218. The search strategy identified 744 titles after removing duplicates. We identified 14 studies that met all eligibility; 7 studies are ex-ante and 7 are ex-post.
Studies have focused on the price and cost of drugs, accessibility, benefits and the speed of drug marketing. Changes in intellectual property policy due to the implementation of trade agreements affect drug prices, expenditures and sales, consumer welfare and, ultimately, the affordability of drugs. The direction and magnitude of price effects differ between ex ante and ex post studies. In addition, the reported effects of policy changes resulting from trade agreements on access to medicines appear to be clearly multifactorial. In the case of TRIPS, life-saving drugs are viewed in the same way as pure consumer products, and the devastating effects of high prices are generally ignored. The balance between the private interests of the patent holder and the broader interests of the company is strongly distorted. It didn`t take long for the subject to end. In 2001, at the WTO`s annual meeting in Doha, Qatar, countries agreed to address this imbalance and strongly reaffirmed the primacy of health over trade interests. The Doha Declaration reaffirmed the right of countries to use TRIPS guarantees, such as compulsory licences or parallel imports, to overcome patent barriers to promote access to medicines, and cited countries in their use. A final important achievement of Doha was to extend from 2006 to 2016 the period until the least developed countries had to issue and obtain pharmaceutical patents.
This period still needs to be extended, otherwise they will face the same difficulties that other developing countries are already facing in terms of access to medicines. Ex ante and ex post methods have advantages and limitations, and for the rest, the rest of the two species report, for the most part, higher prices and reduced consumer well-being by imposing intellectual property protection in trade agreements.